Many computer systems include a microprocessor unit for processing data and an associated monitor for displaying full color video images. Systems which utilize full color monitors or display units typically include analog or digital interfaces, which provide display control functions for the display unit. In this regard, a typical system employs a computer video signal generating source, such as a VGA video card usually employed in a video drive module of a personal computer system. Such a video drive module typically provides analog RGB signals and/or digital RGB signals with accompanying video formatting signals such as HSYNC and VSYNC signals. Other microprocessors may utilize a video drive module for supplying NTSC composite television signals depending upon the type of monitor employed in the system.
Because of the diversity in the different types and kinds of monitors available for such systems, it has been necessary to employ various types of interfaces to accommodate the different kinds of analog and digital video signals, as well as the different types and kinds of signal formats. In this regard, many different types and kinds of interfaces adapted for coupling a video signal producing device to an associated display unit are known in the prior art. For example, reference may be made to the following U.S. Pat. Nos. 4,531,160; 4,536,856; 4,631,692; 4,760,387; 4,779,083; 4,827,255; and 4,886,343.
U.S. Pat. No. 4,536,856 discloses a video signal display control method and apparatus for providing display control functions for an LCD display device to be attached to an external microprocessor providing output video signals. The apparatus employs an algorithm for processing an output composite video signal to permit display device signal information to be presented to the display device on a scaled-up size or a scaled-down size relative to the physical screen of the LCD display device.
U.S. Pat. No. 4,631,692 discloses another interface adapted for coupling an external microprocessor to an RGB type monitor, where the external microprocessor can only provide a television formatted NTSC signal.
While the above discussed U.S. patents may disclose various types of interfaces for coupling video signal producing devices to various types and kinds of display devices, such interfaces have not proven to be entirely satisfactory for some application, where modern high speed, liquid crystal display monitors are employed.
More particularly, conventional high speed RGB liquid crystal display monitors include a plurality of pixel elements arranged in a matrix array. In this regard, each pixel element in the array, includes an associated group of sub-pixel elements for producing different colors, such as the colors of red, green, and blue. Such sub-pixel elements, are so small in physical size, they are unable to be distinguished by the human eye. Thus, by selecting various combinations of the sub-pixel elements, up to eight different colors can be exhibited by each of the pixel elements. Such a small number of displayable colors however, severely limits the performance of a video signal producing device for generating an analog signal indicative of an infinite number of colors.
Thus, while such a technique of displaying eight different colors on an RGB liquid crystal display monitor may be satisfactory for some applications, it is not entirely satisfactory for those applications requiring a large number of colors to be displayed.
One attempt at solving the above-mentioned color limitation problem, is disclosed in U.S. Pat. No. 4,827,255 where a video signal producing device is coupled to an RGB digital display device for producing up to 3375 or 15.sup.3 different color shades. In this regard, a gray scale technique is employed where a series of display patterns having an area of 2 dots.times.2 lines are displayed repeatedly at a cycle or period of every 8 frames.
While such an interface has proven satisfactory for many applications, such an interface is relatively expensive as it requires the utilization of a multiple panel display device, or a multiple number of drivers for each bit of digital information supplied to the liquid crystal panel. Moreover, such an interface and method suffers from loss of color information and creates a repetitive beat pattern so that displayed images tend to flicker.
Therefore, it would be highly desirable to have a new and improved high resolution display system and method for displaying a large number of different color shading levels utilizing a low cost single panel liquid crystal display device, employing low cost single bit drivers. Moreover, such a system should eliminate, or at least greatly reduce, the loss of color resolution and color information.
Another problem associated with prior known interfaces is known as "contouring." In this regard, because an analog RGB signal is indicative of an infinite number of discrete shading levels, it has been difficult to digitize such an analog signal so that color shade differences in the same primary color sufficiently blend to avoid forming lines of separation when displayed.
A well known technique for eliminating or for at least greatly reducing contouring has been to quantize the supplied analog signal with a sufficient number of digital bits, for example with eight digital bits of data, in order to provide a sufficient number of discrete color shading levels to avoid contouring.
While such a technique provides a sufficient number of discrete color shading levels, such a technique has not proven satisfactory for active matrix display panel units which employ only single bit LCD drivers. More particularly, because a sub-pixel element can only be turned on or off, sophisticated duty cycling techniques have been necessary to obtain only a small number of different shading levels of the same color. Such small numbers, of fifteen or less shading levels, have not been sufficient enough to reduce contouring substantially.
Therefore, it would be highly desirable to have a new and improved high resolution display system and method for displaying a large number of different color levels of the same primary color in order to eliminate or to at least greatly reduce contouring problems associated with low cost active matrix display units employing single bit LCD drivers.